The invention relates to a process for acquiring data representative of the shape of an object by detection of the dimensions of a number of contours of said object, which contours are determined by means of successive parallel imaginary planes in which a feeler is constrained to move.
For reproducing complex parts from a machine-tool, a copying technique is often used which consists in taking the dimensions of a model by using a feeler and using this data for controlling the movement of the tool. The copying may be carried out in real time, i.e. by driving the tool at the same time as the feeler explores the model, if the exploration takes place in a period of time compatible with that required for machining. This data may also be recorded on a magnetic support medium of perforated tape once and for all and this memory may be read whenever it is desired to copy the model. This pre-recorded process is more flexible in use to the extent that the speed of reading the information stored on the tape may be adapted to the machining time. A constant problem which is met with the use of this kind of process is to obtain a good compromise between copying accuracy and copying speed.
Systems are known where the exploration is carried out by maintaining a permanent contact between the model and the feeler and recording the coordinates from the feeler at given time intervals. Accuracy of this type of exploration is limited by the deflection of the feeler and by the quality of the positioning control of the two motors controlling the movements of the X-Y table carrying the feeler or the model. More recently, attempts have been made on the contrary to carry out exploration by a succession of contacts between the feeler and the object-model, said feeler exploring an imaginary sectional plane of the object by moving successively away from and towards the object while seeking positions in which there is contact between feeler and object. The accuracy and speed depends on the exploring pitch of the feeler. For a good accuracy, a small pitch is required, but the exploring time is all the longer the smaller the pitch. Whatever the exploration mode, storage of the information representative of the contour is generally made by storing coordinates representative of a number of contact points between feeler and model (and more particularly the coordinates from the center of the end of the feeler when contact is established) and by choosing a linear interpolation between the points (the word pole will be used further on to designate such points) represented by these coordinates. The contour of the object-model is considered as reproduced by a broken line joining together the points of the imaginary sectional plane whose coordinates correspond to contact between the feeler and the object-model.